New Methods To Prepare Cellulose Microspheres And Cellulose Composite Cryogel Microspheres

Cellulose is the most abundant natural polymer, which is relatively inexpensive. Cellulose microspheres with porous structure can be used as the chromatography matrix, immobilization carrier for biomass and so on. With cellulose as raw material, this paper developed new methods, microchannel method and direct injection, to prepare cellulose microspheres and cellulose composite cryogel microspheresFirstly, cellulose microspheres was prepared by microchannel chip with uniform size and used as the chromatography matrix. Ionic liquid,[EMIM]MP, was used to dissolve the microcrystalline cellulose (MCC) to produce cellulose solution. Microdroplets with uniform size were generated by a cross-flow microchannel chip. Then the microdroplets were solidified to obtain the monodisperse cellulose beads. The optimized preparation condition was2%cellulose solution as water phase, the flow rate of water phase of6μl·min-1and oil phase of200μl·min-1. The cellulose microspheres have good sphericity, high porosity and pore volume. Coupled with DEAE as the functional ligand, the cellulose microspheres were used to prepare weak anion-exchange resin. The ion exchange capacity was123.3μmol·g-1. The saturated adsorption capacity of bovine serum albumin could reach220mg·g-1, and the effective diffusion coefficient was1.8×10-11m2·s-1, which showed a potential application for protein separation..Secondly, cellulose was oxidized with2,2,6,6-tetramethylpiperidine-1-oxide (TEMPO). TEMPO-NaClO-NaBr ternary system was used to oxidize microfibrillated cellulose (MFC) and MCC. The contents of carboxyl group and aldehyde group were measured. The amount of NaClO was optimized as5.6mmol·(g-1cellulose). The oxidized MFC had0.51mmol·g-1carboxyl groups and0.25mmol·g-1aldehyde groups, while the oxidized MCC had0.56mmol·g-1carboxyl groups and0.78mmol·g-1aldehyde groups. MCC was more prone to produce aldehyde groups during the oxidization with TEMPO compared with MFC. TEMPO-catalyzed oxidation of cellulose provides the basis for the following preparation of cellulose composite cryogel microspheres.Finally, polyvinyl alcohol (PVA) and PVA-cellulose composite cryogel microspheres were prepared. Frozen methods were used to prepare PVA cryogel microspheres. With direct injection method, the optimized preparation conditions were7%PVA concentration, and the time of freezing has little effect on the PVA cryogel microspheres. With the microchannel method, the optimized preparation conditions were5%PVA concentration, the flow rate of oil phase of120μl·min-1and water phase of10μl·min-1. The diameter of PVA cryogel microspheres obtained was about1.6mm. In addition, the direct injection method was used to prepare PVA-cellulose composite cryogel microspheres. With increasing PVA/MCC ratio, the diameter of microspheres became larger and CV value was smaller. After crosslinked with PVA, MCC may change the internal structure of PVA cryogel and have a certain hole reaming effect. The PVA-cellulose composite cryogel microspheres with a large pore size of about2μm would improve the mass transfer of biomolecules in the pores.